Question: Simplify the following expression: $q = \dfrac{5}{4r} + \dfrac{9}{5r}$
Explanation: In order to add expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $4r$ and $5r$ $\lcm(4r, 5r) = 20r$ $ q = \dfrac{5}{5} \cdot \dfrac{5}{4r} + \dfrac{4}{4} \cdot \dfrac{9}{5r} $ $q = \dfrac{25}{20r} + \dfrac{36}{20r}$ $q = \dfrac{25 +36}{20r}$ $q = \dfrac{61}{20r}$